This invention relates to a method and apparatus for forming splices at the ends of conveyor belts.
Conveyor belts are commonly used as a means to move material from one location to another. In large mining operations, the conveyor belt is generally formed of a rubber body embedded with steel cords or strands. A cover compound can be used at the surface wherein the material is to be conveyed. Generally the compound is very abrasion and cut resistant and of sufficient thickness to prevent the rocks being conveyed from tearing the belt. A pulley compound can be used on the interior surface, this rubber is ideally suited for improved wear as the belt traverses over the pulleys used to drive the belt.
These steel corded or stranded belts may extend several miles and cost millions of dollars to install and fabricate. The fabrication of such belts occurs initially at a factory wherein steel strands or cords are arranged in a coplanar relationship parallel to the surface of the belt so that the belt will exhibit uniform expansion and minimize weaving as it traverses which can cause belt damage.
The prior art method of fabricating belts requires the steps of vulcanizing the rubber belt and winding it onto large spools for shipping to the site. Once the spools of belt are received at the site, the ends must be prepared for splicing by removing the vulcanized rubber from the strands over a distance determined to be sufficient to provide enough joint length to make a secure splice.
Removal of the rubber can be a very time consuming and tedious task. Often times piano wire is used to peel the vulcanized rubber from the strands. In large belts of several feet in width over a hundred strands must be exposed at each joint end. Once exposed, the strands had to be cleaned of as much of the vulcanized rubber as possible. The strands were then cleaned with solvents such as toluene and then a bonding agent was applied comprising a 3:2 mixed solution of xe2x80x9cChemlok No. 203xe2x80x9d and xylene, for example, and rubber cement is applied to the strands and dried. After the preparation of both ends as described in U.S. Pat. No. 3,487,871 entitled xe2x80x9cA METHOD OF JOINING CONVEYOR BELTS HAVING STEEL CORDS EMBEDDED THEREINxe2x80x9d granted Jan. 6, 1970, a joining member is formed made of vulcanized or semi-vulcanized rubber of the same quality as the rubber used in the formation of the belt. The upper face of the member is preferably made of a non-vulcanized rubber and provided with a plurality of strand receiving grooves. Once the strands are in place, a bonding agent of the type described above is preferably coated on the faces of the surfaces to insure complete bonding. While this prior art patent use the term xe2x80x9cnon-vulcanized rubberxe2x80x9d being preferable at the melting surfaces of the otherwise vulcanized or semi-vulcanized member (13), it is believed that the term means xe2x80x9chaving at least its upper surface formed of incompletely vulcanized rubberxe2x80x9d as was required in the claim of the patent. An important limitation when the member for splicing is semi-vulcanized at this grooved surface, the use of semi-cured rubber forced the use of bonding solvents. These solvents are high in VOC""s and the liberal use of xylene and toluene creates carcinogenic risks to the personnel. In developed parts of the world, the use of such solvents is greatly discouraged.
A second limitation of the prior art splicing member is that the member was apparently molded to the exact width of the belt and had exactly twice the number of strands as the belt. This meant that for each belt width, there had to be a unique member since conveyor belts are not standardized in width or in the size or in the number of strands to use the concept taught in that patent required specially designed molds.
A third limitation of the method of splicing described in U.S. Pat. No. 3,487,871 was that the strands had to be free of any of the vulcanized belt rubber which, if left on the strands, adversely affected the bonding.
The most relevant prior art document is considered EP-A-0 372 510 (Stahgruber Grunber and Co. Otto) which has the feature identified in the preamble of independent method claim 4.
An object of the present invention is to eliminate the need to semi-vulcanize the splicing member.
Another objective is to make the use of solvents unnecessary.
Still another objective is to eliminate the need to completely strip the strands of all vulcanized rubber prior to splicing.
A still further objective is to provide a splicing strip that can be used in multiples independent of the width of the belt or the corresponding number of strands.
A still further objective is to improve the splice strength while saving time in splice preparation.
A method of splicing the ends (11, 12) of conveyor belts (10) having vulcanized rubber (2) with steel strands (1) embedded in the vulcanized rubber is disclosed. The method has the steps of (a) removing a portion of the rubber (2) from the belt ends (11, 12) to be joined exposing a plurality of strands (1); (b) providing preformed unvulcanized strips (20) of rubber, in an array of bottom strips (20) each strip (20) having a concave quarter-circular profile wherein strips (20) when laid adjacently to each other form stand receiving grooves (22) located on an upper surface (24), (c) placing exposed strands (1) of the belt ends (11, 12) being joined in the grooves (22) of the bottom strip (20); (d) placing top strips (20) overlying the array of bottom strips (20) and vulcanizing the strips (20) together thereby forming the spliced joint
In a preferred method, the step of removing the vulcanized rubber (2) exposing a plurality of strands (1) includes leaving the strands (1) at least partially sheathed in the vulcanized rubber, most preferably in a coating of the vulcanized rubber (5) whereby the step of vulcanizing the strips (20) together includes vulcanizing the strip (20) to the at least partially sheathed strands (1).
The step of providing at least two arrays of unvulcanized strips (20) of rubber includes the steps of providing at least two bottom strips (20) and positioning the strips (20) adjacently to increase the width of the strips (20), and cutting one of the at least two bottom strips (20) parallel to the grooves (22) thereby substantially matching the total width of the adjacently layered strips (20) to the conveyor belt width (WB).
The array of top strips (20) of similarly grooved as the array of bottom strips (20). Preferably, the top and bottom strips are the same in cross-sectional profile.
The step of providing the top or bottom strips (20) includes the steps of extruding the strip (20), the extruder having a die (356) having a predetermined cross-section for forming the strips (20) forming the strand receiving grooves (22) of the upper surface (24).
Each strip (20) has a predetermined cross-sectional profile having a flat base, a first side and a second side extending between the flat base and an upper surface, the first side having a concave surface having a quarter-circular shape or depression intersecting the top surface and extending along the length of the strip (20).
In one alternative embodiment, the second side has a substantially straight profile. In the preferred embodiment, the second side has a concave surface having a quarter-circular shape.
Each of the above methods of splicing uses an unvulcanized elastomeric strip (20) for splicing steel cable reinforced belts (10), the strips (20) having a base (WS) and length (LS). The strips (20) are characterized by an uncured strip (20) having a predetermined cross-sectional profile having the base (WS), an upper surface, a first side and a second side, each side extending between the base and an upper surface. The profile having two substantially quarter-circular depressions extending parallel along the length of the strip, each depression providing substantially half of a steel cable receiving groove (22) for placement of a steel cable or strand (1).
It is preferred that strips (20) has a width of the base (WS) requiring a plurality of strips (20) for each splice joint.
Most preferably, the strips (20) are prepackaged in spools of continuous lengths of four or more strips (20) for each splice joint.